Driving piles into the bed of a body of water produces a high level of noise in the surrounding environment. The noise increases alongside an increase in the diameter of the piles and in the depth of the bed of the body of water, to the point of exceeding the threshold tolerated by Cetacea and Pinnipedia. For this reason, some countries have imposed a maximum noise threshold. For example, the threshold imposed by the German government is 160 dB re 1 μPa at a distance of 750 meters.
One way of reducing noise is to use a contact damper between the free end of the pile and the pile driver. That is, the contact damper acts as a shock-absorber, which reduces the force of impact and, with the reduced force, the noise level by roughly 5-10 dB. Using this solution, however, more blows are needed to drive in the pile.
Another way of reducing noise is to alter the operating parameters of the pile driver and, more specifically, to prolong the time the pile driver ram remains in contact with the pile, so as to reduce vibration of, and the noise produced by the pile. This solution, however, also has the drawback of requiring more blows to drive in the pile.
Another pile driving noise abatement solution currently being researched is to generate air bubbles around the pile.
A few examples of noise abatement techniques are described in U.S. Published Patent Application No. 2002080681, U.S. Published Patent Application No. 2011031062, U.S. Published Patent Application No. 2013001010, German Patent No. 10302219 and German Patent No. 10117109.
PCT Patent Application No. WO 2010/151121 discloses a double walled device for the passive reduction of the sound vibrations in a liquid resulting from a sound source arranged below the liquid level of a body of water. The double walled device defines a sealed intermediate space between the walls and is inserted into the body of water via adjustable anchors.